Addition agent and its use in the treatment of iron and steel



Patented-Jan. 6. 1942,

I summon AGENT-AND us use m was uni-moor mos an arm June a. crime.Dourluton. and Walter Falls, N. Y... salmon to Elec- Cratts. Niagara troMetallurgical Company, a'corporation of No Drawing.

Original application lepru 14.1w, Serial No. 201,031. Divided and um appication December 1,1938. Serial No. 243,825

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. The invention relates to the treatment 01 molten iron and steel topromote a line grain structure and freedom fromdeleterious impurities.application is a division of our application Serial No. 201,931, filedApril 14, 1938.

During manufacture, steels become contaminoted with certalnoxides andoccluded gases, which, ii not substantially removed or renderedinnocuous, detrimentally affect the soundness and physical properties oithe finished steel. To overcome the deleterious efiects of suchimpurities, an addition of ferrosillcon or ten-omensanese, or both, asdeoxidizers, is usually made to the steel shortly before casting intoingots or other shapes. For further deoxidatlon, and to provide aninherently fine-grained steel having inhibited grain growth tendenciesat elevated temperatures, a later addition of aluminum is often made tothe molten steel.

Aluminum additions, in the amounts, for the pur oees, and in the mannerdescribed above, tend to produce a steel containing deleterious typesand quantities oi non-metallic inclusions. it has been proposed tosubstitute for the aluminum other agents, such as vanadium, or titanium,

but none of these elements is entirely satisfactory.

Vanadium is usually too expensive to add in an amount suificient toproduce the desired results. and titanium as heretofore used tends toproduce a steel containing numerous objectionable nonmetallicimpurities.

, According to the present invention, a steel that ssubstantially freefrom deleterious, gaseous or solid non-metallic impurities and that hasimproved'mechanicai properties (including improved impact strength) andexcellent fine grain characteristics is produced by adding to the steelwhile it is molten in the ladle or otherwise shortly before casting, anaddition agent containing 50% to 55% of silicon. remainder iron and atleast two elements selected from the following two groups: (1) titanium,zirconium, cerium,

hafnium, and thorium; (2) vanadium, columbium, and tantalum, at leastone element being present from each group, each in an amount at leest3%. Iron is present as an impurity or diluent unavoidably introduced inproducing an economical and commercially practicable material. The totalamount of the elements selected irom the groups herein described ispreferably at least 10% of the composition of the addition agent. If thenumber of elementsdn said mixture is only two, said total amount shouldpreferably not exceed 25% of the composition of the addition agent, andif such number is more then This two, said total amount preferablyexceeds 25% by not more than 5% for each of said elements above' two. Apreferred addition agent compositlon contains 50% to silicon, 5% to 15%gconium, 5% to 15% vanadium, the remainder n. r The constituents of theaddition agent are preferably presllcyed in the form of a master alloy;but they may be unalloyed or only partielly alloyed, and used in theform of a briquet of comminuted material. Also, some of the constituentsthereof may suitably be in the form 01' easily reducible or decomposablecompounds such m nitrides, nitrates or mixtures thereof. It isessential, however, that the constituents be closely associated, becausesuccessive additions of the several constituents separately to the steeldo not yield the improved results of the invention.

in general, the more complex the addition agent, that is, the greaterthe number of deciddizing ingredients, selected from the above groups,the better the results.

ln'practicins the processor the invention, we

prefer to add to the molten steel being treatedv a sumcient amount ofthe addition agent of the invention that the silicon content of thesteel is increased by about 6.25%. The deoxidizing or groin refiningpower may be controlled and varied by adding more or less than enoughmaterial to increase the silicon content of the steels by about 0.25%,or alternatively, the concentra-' tion of silicon relative to the otherconstituents of the addition agent may be varied. If less grainrefinement is required, part oi the silicon required for deoxidizing maybe added as the agent of the invention and part as ordinaryferrosilicon, and if more grain refinement is required, the action ofthe addition agent may be supplemented by an addition of aluminum orother grain refiner.

The desired composition may be added to the steel in any well knownmanner, for example, in the furnace, in the ladle, or in the moltenstream during pouring. If the agent is added to the steel in thefurnace, the iron content of the agent may be greater than 50%.

By proper selection of elements, a grain size of No. 6 or No. '7 mayreadily be procured in steels treated according to a method of theinvention. Throughout the present specification, grain size refers toaustenitic or inherent grain size determined by the McQuaid-Ehncarburizing test conducted at a temperature of 925 C. for 8 hours, asdefined by the A. S. T. M. specification Elli-33. The degree of grainrefinement or deoxidation of the steel per unit of addition agent addedwill vary, not only with the combination of elements selected, but alsowith the type of steel being treated, o that the total amount of agentto be addedto the steel for best results mustbe determined by trialOrdinarily, this total amount of'agent will be less than 5%, and mostfrequently less than 1%.

While the addition agents of this'invention are especially useful in thetreatment of steels which are to be hot worked, the invention is alsoapplicable to the treatment of steels which are to be employed ascastings. Used for the latter purpose, it has been found that, in manyinstances, the characteristics of the casting may be improved if thematerial of theinvention is 7 added in an amount which is'sumcient to deoxidize the metal, yet is rnsumcaem to' develop harmful inclusions.

. Steels treated according to the invention are sound, substantiallyfree from excessive nonmetallic'inclusions, and possess improvedductility and shock resistance. Further, the few inclusions distributedthroughout such steels are more uniform than diverse, that is. themajority of the inclusions which usually accompany any deoxidizingtreatment that produces small grain size are not noticeable in thesteels deoxidized in accordance with the invention until a higher degreeof grain refinement is attained than that attainable by the addition ofaluminum alone.

We claim: i. A composition of matter for use as an addition agent fortreating molten ferrous metal. composed of between 50% and'85% silicon;at least one element of the group consisting of titanium, zirconium,cerium, hafnium, and tbor-r ium, in an aggregate percentage between 5%and 20%; at least one element of the group consisting. of vanadium,columbium, and tantalum, in an aggregate percentage between 5% and 20%;

=the sum of the percentages of all elements of both of such groups beingnot over 25%; and iron .as the remainder.

2. A method of treating molten steel which 7 comprises adding thereto agrain-refining pro- JAMES H. CRITCHE'I'I'. WALTER CRAFTS.

